CH test, buffer needed?

Miranda

Well-known member
Jan 20, 2008
161
Northeast Florida
I have never added the buffer solution when testing for CH, in fact, I never knew it existed until I read the instructions recently. Is it mandatory? My old test kit (Walmart?) had two vials, A &B, no buffer. I replaced it with Taylor reagents which I think are the same as A & B as they perform the same, but the instructions also include a third vial, the buffer solution which is NaOH. Can I do without this step? The only issue I ever noticed (with both kits) is sometimes if the pH is low the test doesn't work properly. the sample turns yellow instead of pink, however, I have found that if I just leave the sample out for a few minutes it turns pink and then the test works properly, I guess because the ph rises a bit on standing.
 

Bama Rambler

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Jun 22, 2009
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SouthWest Alabama
I would recommend you use the buffer solution. If the R-0??? numbers are the same then they are the same reagents. They include the buffer to insure a better result fromk the test.
 

Miranda

Well-known member
Jan 20, 2008
161
Northeast Florida
I think the reagents from the Walmart kit are the same chemical as the Taylor reagents based on the way they behave and change color, however, the Walmart reagents aren't numbered,they are just A&B so who knows. Just wondering if the Buffer is really only needed for low pH water (below 7.2) . For normal pH water, I get exactly the same results with or without the buffer.
 

JasonLion

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May 7, 2007
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The WalMart test kit follows the same basic design as the full Taylor test kits, but it uses simplified, less expensive, reagents that are noticably more sensitive to interference.

The buffer solution helps prevent interference from metals, most commonly iron, from affecting the test results. If there isn't anything in your water that might interfere, the result will be the same without the buffer. I wouldn't count on that always being true. It is best to use do the test in the way it is designed to be done.
 

Miranda

Well-known member
Jan 20, 2008
161
Northeast Florida
That makes alot of sense. I have another question concerning titrations. For CH, directions say to add reagent dropwise until color changes from red to blue. Likewise, for TA the directions say to add dropwise until color changes from green to red. In both tests, there is an "in between". For an example: 9 drops-still definately green, 10 drops greenish gray, 11 drops gray, 12 drops pinkish gray, 13 drops definately pink. What is the most accurate TA? 120 for the first evidence of pink? Or 130 for complete color change?
 

JasonLion

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May 7, 2007
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130. Once the color starts changing, you continue adding drops as long as the color continues changing. The final drop, that does not change the color any further, does not count.
 
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